This invention relates to leads for use with dual chamber pacemakers and, more particularly, to a single lead system and method of using same for providing at least ventricular stimulation and also providing atrial sensing through two spaced floating bipoles located on the lead.
Dual chamber pacemakers are recognized to have a greater capacity for optimum physiologic stimulation of the heart than single chamber devices, for many patients. However, dual chamber systems conventionally require implantation of two intracardiac leads, which has long been widely viewed as an obstacle. A dual chamber system using a single multipolar lead to sense the atrium and to stimulate the right ventricle, i.e., operating in a VDD mode, can avoid the difficulties related to separate atrial lead implantation. Such VDD stimulation using a single lead for atrial sensing and ventricular pacing has become a reality. During the last decade, several such systems for permanent atrial sensing and pacing have been tested. More recently, new types of multipolar leads have been developed using novel arrangements where electrodes are positioned on the atrial floating portion of a single right ventricular catheter. See, for example, the paper of Goldreyer et al., "A New Orthogonal Lead For P-Synchronous Pacing," PACE, 1981, 4:638-644; Goldreyer et al., "Orthogonal Electrogram Sensing," PACE, 1983, 6:464-469; Brownlee, "Toward Optimizing the Detection of Atrial Depolarization With Floating Bipolar Electrodes," PACE, 1989, 12:431-442.
At the present time, a half-ring electrode system is commercially available. This system consists of a unipolar VDD pacemaker and a single lead with a ventricular pacing electrode and a single supplementary half-ring bipole on its proximal atrial floating portion. Also, pacemakers have been introduced with Holter capabilities for monitoring and storing cardiac rhythm abnormalities, although these capabilities are generally limited to certain simple arrhythmias. Thus, the detection of the atrial electrogram (AEG) and the technical means for Holter monitoring and storage, are generally known in the prior art.
However, these systems have not proven reliable with respect to several crucial variables. For example, any reliable VDD system needs to provide an AEG with an acceptable minimum level. Also, it is important that atrial sensing have a high ventricular far-field rejection. As used herein ventricular far-field rejection is calculated by dividing the mean atrial electrogram amplitude, AEG, by the corresponding mean ventricular electrogram amplitude (VEG). Also, it is desirable to have means for obtaining more diagnostic information, including reliable means for measuring the intra-atrial P-Wave direction and conduction time, and recording same. Also, it would be desirable to have a single lead system with which the atrium could also be paced, thereby providing dual chamber pacing capability.